This invention is directed to lamps, and is particularly directed to apparatus for varying the intensity of a light source without changing its color quality.
In motion picture production, it is often advantageous to vary the amount of light on a subject. Such an instance occurs when the subject is moved closer to the camera and light source during filming. Certain electrical controls, including rheostats, have been successfully employed for varying the intensity of light. However, as the intensity is varied, the color quality changes with such devices. This change may be imperceptible to the human eye; however, color film is easily affected by a color quality change. Shutters and other similar devices are also not highly practical as they tend to cast shadows on the object being photographed. These problems are especially acute in motion picture production with lights used very close to the camera as a means for relieving shadows on the subject. Naturally, problems resulting from changes in light intensity may arise in other than motion picture production.